The Frequency Comb (R)evolution. Thomas Udem Max-Planck Institut für Quantenoptik Garching/Germany

Transcription

1 The Frequency Comb (R)evolution Thomas Udem Max-Planck Institut für Quantenoptik Garching/Germany 1

2 The History of the Comb Derivation of the Comb Self-Referencing 2

3 3

4 Mode Locked Laser as a Comb Generator Typical Ti:sapphire Kerr-lens mode locked laser: -pulse repetition ratet -1 = 100 MHz 1 GHz -pulse duration = 10 fs -spectral width = 1/ = 100 THz - N = modes phase synchronized 4

5 The History of the Comb 5

6 The First Continuous Wave Laser William Bennett and Ali Javan with the first continuous wave laser

7 Coherent Waves with Frequencies? Scully, Zubairy - Quantum Optics 7

8 Laser Beat Notes 8

9 Laser Beat Notes 9

10 Increasing the Measureable Frequency Difference direct measurement of optical beat frequencies is limited by the detector bandwidth to a few 100 GHz wit h some tricks to a few THz. 10

11 11

12 Stanford Mode Locked Laser 1978 A.Ferguson J.Eckstein T.W.Hänsch J.Goldsmith E.Weber Carrier envelope offset phase and frequency described in detail in Jim Eckstein s Thesis Stanford

13 Frequency Differences and Absolute Frequencies 890 GHz 13

14 Harmonic Frequency Chains Boulder Novosibirsk 14

15 Harmonic Frequency Chains 15

16 How to Improve the Optical Counter 16

17 Kourogi Type Frequency Comb Generator 17

18 Kourogi s Comb Generator in our Lab Opt. Lett. 23, 1387 (1998) 18

19 Optical Interval Dividers f 1 f 3 f 2 f 1 f 3 f 2 Optical Interval Divider (Differential Gear) T.W.Hänsch in The Hydrogen Atom G.F.Bassani, M.Inguscio, T.W.Hänsch eds, Springer

20 Optical Counter 20

21 Phase Noise 21

22 Phase Noise: Why the Comb shouldn t work 22

23 Phase Noise: Why the Comb shouldn t work 23

24 Phase Noise Th. Udem, lab book

25 Phase Locked Loop 25

26 Testing the Mode Spacing Constancy 26

27 Testing the Mode Spacing Constancy 27

28 Derivation of the Comb (from the pulse train) 28

29 Mode Locked Laser 1 n = n1 r + 1 m 1 CE = m1 with r 1 CE < 1 r 29

30 Mode Locked Laser E(t) = A(t) e i1 ct = A m e im1 rt i1 c t m I (1) 1 c 1 1 m = m1 r + 1 C 30

31 Spectrum of N+1 Pulses (shift theorem) 31

32 Spectrum of N+1 Pulses 32

33 Fourier limited Line Width of the Modes 33

34 Line Width of real Lasers 34

35 Resolving the Modes of the Comb 35

36 Self-Referencing 36

37 How to Measure the Comb Offset Measure any frequency difference between different harmonics of the same laser (or comb). 37

38 Carrier-Envelope Phase

39 The first self-referenced Frequency Comb 3.5f -4f self-referencing (N=7, M =8) 39

40 Generating an Octave Spanning Comb Photonic crystal fiber: William Wadsworth Jonathan Knight Tim Birks Phillip Russell U. of Bath England note: if the action of the fiber is the same for all the pulses the field stays stricly periodic. This property is the only one necessary to derive 1 n = n1 r + 1 CE 40

41 A much more compact Device f -2f self-referencing (N=1, M =2) 41

42 Compact Ringlaser -wedge and EOM for slow and fast 1 CE cont rol. -translation stage and PZT for slow and fast1 r cont rol. 42

43 Simplest way of Self Referencing: M =2 N=1 It is simple to detect 1 CE of an oct ave wide frequency comb: 1 CE = 2(n1 r + 1 CE ) (2n1 r + 1 CE ) J. Reichert et al., PRL 84, 3232 (2000) 43

44 Fiberlaser -pump power controls1 CE -fiberstretcherfor1 r cont rol 44

45 Fixpoint Concept I fixpoint at 1=0 Cavity length L elast ic t ape : (n1 r + 1 CE ) (1 + L/L)

46 Fixpoint Concept II fixpoint at m = 0 (1= 1 C ) Pump power accordion : m1 r (1+ ) + 1 C Fixpoint important for locking and noise compensation! Better to enumerate mode number m from fixpoint.

47 Controlling the Frequency Comb depends on the cavity length 1 n = n1 r + 1 CE depends on the pump power we can measure and cont rol 1 r = 2 /Tand 1 CE = 7/T 47

48 Optical Frequency Counter locked to a Cs atomic clock 1 n = n1 r + 1 CE every mode can be used for opt ical frequency measurement a million st abilized lasers in a single beam! 48

49 Frequency Conversions with the Comb radio frequency or optical frequency radio frequency optical frequency locked to a Cs clock optical frequencies optical frequency locked to a stable laser radio frequency locked to countable clock output radio frequency or optical frequency optical frequency locked to a stable laser measure another laser optical frequency locked to Science 293, 825 (2001) 49

50 Thank you for your Attention 50